合并k个排序链表

  Definition for singly-linked list.
  public class ListNode {
      int val;
      ListNode next;
      ListNode(int x) { val = x; }
  }
 */
class  {
    public ListNode mergeKLists(ListNode[] lists) {
        if(lists==null||lists.length==0)
            return null;
        PriorityQueue<ListNode> queue=new PriorityQueue<ListNode>(lists.length,new Comparator<ListNode>(){  
           public int compare(ListNode o1,ListNode o2)
           {
               if(o1.val<o2.val)
                   return -1;
                else if(o1.val>o2.val)
                return 1;
           else
              return 0;
           }
       });
        
        ListNode dummy=new ListNode(0);
        ListNode tail=dummy;
        
        for(ListNode node:lists)
        {
            if(node!=null)
                queue.add(node);
        }
        while(!queue.isEmpty())
        {
            tail.next=queue.poll();
            tail=tail.next;
            if(tail.next!=null)
                queue.add(tail.next);
        }
            return dummy.next;                                            
    }
}